The situation at Japan's crippled nuclear complex in Fukushima 240km north of Tokyo remains “grave and serious,” prime minister Naota Kan said today.
In a televised address Mr Kan warned that “we are not in a position where we can be optimistic. We must treat every development with the utmost care”.
He apologized to farmers and business owners around the plant for damage caused.
Two Japanese travelers arriving in China today were found to have high radiation levels in the latest consequence of contamination from a crippled nuclear plant two weeks after the Asian nation's devastating earthquake and tsunami.
China's customs body said the pair had medical treatment for radiation levels "seriously" over the limit, but they did not present a risk to others after flying to Wuxi in the east.
Until now no one in Japan except workers at the stricken plant has been found with seriously elevated radiation levels, and Japan's foreign ministry noted that as of March 18 the International Civil Aviation Association had declared that screening of airline passengers from Japan was not necessary.
The first case of contaminated Japanese traveling abroad came after injuries to workers slowed the battle to control the nuclear complex.
Some 700 engineers have been working around the clock to stabilize the six-reactor plant since the multiple disaster on March 11 that also left more than 27,000 people dead or missing.
But they had to pull out of some parts of the complex when three workers replacing a cable at one reactor were exposed to high contamination by standing in radioactive water yesterday, officials said.
Two were taken to hospital with possible radiation burns after the water seeped over their boots.
"We should try to avoid delays as much as possible, but we also need to ensure that the people working there are safe," said Japanese nuclear agency official Hidehiko Nishiyama.
Safety fears at the plant and beyond - radiation particles have been found as far away as Iceland - are compounding Japan's worst crisis since the second World War.
As well as causing the most serious nuclear accident since Chernobyl in 1986, the magnitude 9.0 quake and ensuing wall of water that tore in from the Pacific killed 9,811 people and left 17,541 more missing, according to latest police figures.
Kyodo news agency said the death toll had topped 10,000.